Dual mode band-pass filter

Abstract

A dual mode band-pass filter includes a metallic film for defining a resonator, disposed on the first main surface of a dielectric substrate having first and second main surfaces, or inside of the dielectric substrate. An opening is formed in the metallic film. At least one ground electrode is provided on the second main surface of the dielectric substrate or inside of the dielectric substrate, so as to be opposed to the metallic film through a dielectric layer. A pair of input-output coupling circuits is connected to the metallic film.

1. A dual mode band-pass filter comprising:
 a dielectric substrate having first and second main surfaces; 
 a metallic film having one of a cross-shaped opening, an opening with bent portions and a plurality of openings, and disposed on the first main surface of the dielectric substrate or inside of the dielectric substrate; 
 at least one ground electrode disposed on the second main surface of the dielectric substrate or inside of the dielectric substrate, so as to be opposed to the metallic film with the dielectric substrate disposed therebetween; and 
 a pair of input-output coupling circuits connected to different portions of the metallic film; wherein 
 the metallic film consists of only a single metallic film; 
 the opening in the metallic film has a longitudinal dimension that extends in a direction that is substantially parallel to an imaginary line passing through connection points at which the pair of input-output coupling circuits are connected to the metallic film; 
 the metallic film includes at least a first vertex and a second vertex; 
 the first vertex and the second vertex are disposed at end portions of a first straight side of the metallic film; 
 one of the different portions to which one of the pair of input-output coupling circuits is connected is located between the first vertex and the second vertex of the metallic film; 
 a length of a first portion of the first straight side between the first vertex and the one of the different portions to which one of the pair of input-output coupling circuits is connected and a length of a second portion of the first straight side between the second vertex and the one of the different portions to which the one of the pair of input-output coupling circuits is connected are different from each other. 
 
   
   
     2. The dual mode band-pass filter according to  claim 1 , wherein the dielectric substrate is made of BaO—Al 2 O 3 —SiO 2 . 
   
   
     3. The dual mode band-pass filter according to  claim 1 , wherein the at least one ground electrode is provided on substantially the entire second main surface of the dielectric substrate. 
   
   
     4. The dual mode band-pass filter according to  claim 1 , wherein the metallic film is made of copper. 
   
   
     5. The dual mode band-pass filter according to  claim 1 , wherein the metallic film has the cross-shaped opening. 
   
   
     6. The dual mode band-pass filter according to  claim 2 , wherein the cross-shaped opening is defined by two substantially rectangular openings that cross each other at a right angle. 
   
   
     7. The dual mode band-pass filter according to  claim 1 , wherein the metallic film and the one of the cross-shaped opening, the opening with bent portions and the plurality of openings are configured such that first and second resonance modes of the dual mode band-pass filter are coupled. 
   
   
     8. The dual mode band-pass filter according the  claim 7 , wherein the first and second resonance modes have different resonance frequencies. 
   
   
     9. The dual mode band-pass filter according to  claim 1 , wherein the dielectric substrate is made of fluororesin. 
   
   
     10. The dual mode band-pass filter according to  claim 9 , wherein the fluororesin has a dielectric constant εr of about 2.58. 
   
   
     11. The dual mode band-pass filter according to  claim 1 , wherein the metallic film has the opening with bent portions. 
   
   
     12. The dual mode band-pass filter according to  claim 11 , wherein the bent portions of the opening with bent portions extend in a direction that is substantially perpendicular to the imaginary line passing through the connections points at which the pair of input-output coupling circuits are connected to the metallic film. 
   
   
     13. The dual mode band-pass filter according to  claim 12 , wherein the bent portions extend from ends of a longitudinally extending portion of the opening. 
   
   
     14. The dual mode band-pass filter according to  claim 1 , wherein the metallic film has the plurality of openings, at least one of the plurality of openings having a longitudinal dimension that extends in the direction that is substantially parallel to the imaginary line passing through the connections points at which the pair of input-output coupling circuits are connected to the metallic film. 
   
   
     15. The dual mode band-pass filter according to  claim 14 , wherein each of the plurality of openings are substantially the same size. 
   
   
     16. The dual mode band-pass filter according to  claim 14 , wherein each of the plurality of openings are arranged substantially parallel to each other.